Method for introducing an internal helical formation into a flexible tubular material

ABSTRACT

There is disclosed a method for introducing a helical formation ( 11 ) into a flexible tubular material ( 12 ). The material ( 12 ) is supported together with a surrounding helical former ( 13 ) so as to deform the material ( 12 ) to have a helical indentation ( 11 ) corresponding to the shape of the former ( 13 ). The material ( 12 ) is then set in that configuration and the former ( 13 ) is removed.

FIELD OF THE INVENTION

[0001] This invention relates to a method for introducing an internalhelical formation into a flexible tubular member.

DESCRIPTION OF THE PRIOR ART

[0002] WO 00/38591 discloses the concept of helical formations in tubesfor the purpose of improving in certain desirable respects the flow offluid through them.

[0003] In particular, blood flow tubing, such as vascular grafts, canbenefit markedly from internal helical formations such as ridges orgrooves, which, if appropriately configured having regard to the tubedimensions and the density, viscosity and flow rate of bloodtherethrough, can eliminate turbulent flow and dead regions which canlead to plaque formation, which, in turn, can lead to reduced flowcapacity or thromboses.

SUMMARY OF THE INVENTION

[0004] However, one of the problems with implementing this is how toform the helical formation within the tube.

[0005] In accordance with a first aspect of the invention, there isprovided a method for introducing an internal helical formation into aflexible tubular material, the method comprising supporting the materialon a mandrel having a groove, placing a helical former corresponding tothe groove around the material so as to deform the material to have aninternal helical formation corresponding to the shape of the groove,setting the material in that configuration, and removing the former andthe mandrel.

[0006] In accordance with a second aspect of the present invention,there is provided a tube for a human or animal body, the tube comprisinga flexible tubular material, a side wall of the tube being deformed toform a helical formation in the Internal surface of the side wall of thetube.

[0007] The term “helical” as used herein covers the mathematicaldefinition of helical and any combination of the mathematicaldefinitions of helical and spiral.

[0008] The material is effectively clamped between the mandrel and theformer.

[0009] In one example, the material may be supported in a surroundingstructure together with the former—the surrounding structure maycomprise a cage such as a wire helix.

[0010] Whilst, as compared to the multi-start helical formulationsproposed in WO 00/38591, the method of the present invention isparticularly adapted to the introduction of a single start helicalformation, it is found that such a formation is remarkable effective. Ofcourse, the method of the invention could readily be adapted to theintroduction of multi-start helical formations, if required, either byhaving a multiple former arrangement or by using a single formerrepeatedly with an appropriate angular shift.

[0011] Typically, the tubular material may be thermoplastic orthermosetting, and the material may be set by heat setting. Typically,the material is of a woven or knitted structure in polyester. However,other materials such as PTFE and polyurethane, can be spun or extrudedto the required shape.

[0012] For vascular prostheses, it may be important to provide a degreeof extensibility, so that the prosthesis may be under some tensionbetween the anastomoses

[0013] Any heat setting operation should leave the tubular material,therefore, still elastically extensible.

[0014] In order to provide the correct helix angle in a prosthesis inits tensional configuration, the material may be pre-tensioned for theintroduction of the formation.

[0015] The material, after the formation has been set into it, may becoated with a biocompatible dispersion, eg. with polyurethane.Typically, the former creates a groove in the external wide wall of thetubular material, and the dispersion is introduced into the groove inthe external side wall. This helps to ensure that the internal formationmaintains its shape.

[0016] Preferably, the dispersion is pressed into the material buttypically does not penetrate the material to the inside surface.Preferably, the penetration is at least 50%, but less than 100%, andmost preferably, 80% to 90% penetration.

[0017] A strand of a second material, which may have a different modulusof elasticity to the tubular material, may be introduced into andsecured in the external helical formation after the setting operation.The strand may be a monofilament or a multifilament strand. The strandmay be secured by a subsequent coating.

[0018] The effect of the strand will be an extension of the finishedprosthesis for implant, to introduce a modular formation to theprosthesis, mimicking natural blood vessels.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Method of introducing an internal helical formation into aflexible tubular material in accordance with the invention will now bedescribed with respect to the accompanying drawings, in which:

[0020]FIG. 1 is a view of a helical former for use in the method;

[0021]FIG. 2 is a view of a helically grooved mandrel for use in onemethod according to the invention;

[0022]FIG. 3 is a cross-section through the mandrel of FIG. 2, with thematerial and former in place;

[0023]FIG. 4 is a view of a cage, with former in place, in a secondmethod according to the invention;

[0024]FIG. 5 is a cross-section of a helically deformed tube with afilament insert;

[0025]FIG. 6 is a cross-sectional view of a tube after forming of thehelical formation and having a polyurethane dispersion applied;

[0026]FIG. 7 is a cross-section view of the tube of FIG. 6 with a formerbeing used to press the polyurethane dispersion into the material of thetube;

[0027]FIG. 8 is an enlarged view of section A of FIG. 7; and

[0028]FIG. 9 is a perspective view of a vascular graft manufacturedusing the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]FIG. 1 shows a helical former 13. FIG. 2 shows a mandrel 14 havinga helical groove 15 formed in the external surface of the mandrel 14.The helical shape and cross-sectional shape of the former 13 correspondsto the helical shape and cross-sectional shape of the groove 15.

[0030]FIG. 3 illustrates a method of using the former 13 and the mandrel14 to form an internal helical formation 11 in a tubular material 12 toform a vascular graft 30 (see FIG. 9). The tubular material 12 issupported on the mandrel 14 with the groove 15 corresponding to theconfiguration of the helical former 13. The material 12 is effectivelyclamped between the mandrel 14 and the former 13, and forced into thegroove 15 by the former 13. For example, the mandrel 14 may be stainlesssteel and the former 13 may be PTFE.

[0031] Initially, the material 12 is placed on a straight (non-grooved)mandrel (not shown) and a thread is wound around the outside of thematerial 12. The ends of the material 12 are then pushed together sothat the material 12 is concertinaed. The friction between the material12 and the mandrel maintains the material in the concertinaedconfiguration. The material 12 is then heat set at 95° C. to 105° C. for3 to 4 hours. The thread may be removed before or after heat setting.

[0032] After this first heat set, the concertinaed material 12 is placedon to the mandrel 14 and the former 13 wound around the material, sothat is engages with groove 15 in the mandrel 13 and the material 12 isclamped in the groove 15 between the mandrel 14 and the former 13. Thematerial 12 is then heat set again at approximately 95° C. to 105° C. toset a helical formation 11 corresponding to the groove 15 and former 13.

[0033] Typically, before applying the former, tension is applied to thematerial 12 and this tension is maintained while the former 13 is woundaround the material 12 and mandrel 14. Hence, during the second heatset, the material 12 is heat set with pretension. This allows a degreeof flexibility but helps prevent further extension of the material 12,which would change the helix angle of the helical formation 11. It alsominimises the risk of graft movement or longitudinal extension postsurgery.

[0034] After forming of the helical formation 11, a polyurethanedispersion 22 is applied (see FIG. 6) to the corresponding indentationon the external side wall of the material 12 by an applicator 20. Aformer 21 (see FIG. 7) is then used to press the polyurethane into thematerial 12. However, the polyurethane 22 is not pressed by the former21 so that it penetrates all the way through the material 12. Typicallythe penetration of the polyurethane 22 into the material 12 will beapproximately 80% to 90% of the thickness of the material 12. Inaddition, the amount of polyurethane 22 applied, the shape of the former21 and the pressure applied by the former 21 are chosen such that thepolyurethane 22 overflows the external indentation of the helicalformation 11. In one example, the overflow, S, is approximately 2 mm to3 mm over the edge of the indentation (see FIG. 8).

[0035] The material 12 is then removed from the mandrel 14 and thefinished article can be used as a vascular graft 30 (see FIG. 9) in thehuman or animal body.

[0036]FIG. 4 illustrates an alternative method of forming the helicalformation 11, in which the material 12 is supported in a surroundingstructure 16 together with the former 13. The surrounding structure 16is in the form of a helical wire cage.

[0037] Although, in the example described above, heat setting is used inboth the first and second settings of the material 12, any other settingmethod appropriate to the material may be used. For example, appropriatesetting methods may include chemical, infra-red or ultra-violet settingmethods, or any method that initiates or effects cross-linking in apolymer is a possibility.

[0038] However, it is desirable that, especially in the case of avascular prosthesis, the finished product is elastically extensible, soas to be tensioned between the anastomoses. Generally, a tensionresulting from a stretch of 10% of its maximum extensibility would beappropriate.

[0039] The correct helix angle of the indentation, namely the angle thatgives, on theoretical, trial and error or whatever other appropriategrounds the best result in terms of the elimination of turbulent flowand dead flow areas in and downstream of the implant, the material 12can be pre-stretched for the indentation by the 10% or other appropriateamount without significantly altering the effectiveness of theindentation.

[0040] The material 12 may be coated, after the indentation, for anyreason. It may be that the material, which may, for example, be a wovenor knitted polyamide or polyester, is coated with a bio-compatiblematerial such as a polyurethane.

[0041] In another example (see FIG. 5) a strand 17 may be incorporatedinto the indentation and sealed therein by the polyurethane dispersion22 or by an overall coating, or a “local” coating or glue. The strand 17may comprise a monofilament, for example, of polyester, or it may be amultifilament strand. This can help to maintain the shape and integrityof the indentation, but can also have another effect, namely that onsuch extension as is required to give proper implant tension, thepresence of the strand will imply an undulation to the tube, mimickingnatural blood vessels.

[0042] Clearly, more than one helical “start” may be applied, as byhaving multiple helical formers or by applying a single such former twoor more times each angularly displaced for all previous applications.

[0043] While the invention has been described particularly withreference to blood flow tubing and, more particularly, with regard toimplants, it is possible to provide process plant pipework with internalspiral formations by similar means. In particular, if pipework iscapable of deformation, it might well be given an internal helicalformation by wrapping around it a helical former and pressing the formerinto the pipe, eg. by thermal contraction.

We claim:
 1. A method for introducing an internal helical formation intoa flexible tubular material, the method comprising supporting thematerial on a mandrel having a groove, placing a helical formercorresponding to the groove around the material so as to deform thematerial to have an internal helical formation corresponding to theshape of the groove, setting the material in that configuration, andremoving the former and the mandrel.
 2. A method according to claim 1,in which the material is supported in a surrounding structure togetherwith the former.
 3. A method according to claim 1 or claim 2, in whichthe material is thermoplastic or thermosetting and the material is setby heat setting.
 4. A method according to claim 1, wherein the materialis woven.
 5. A method according to claim 1, wherein the material isknitted.
 6. A method according to claim 1, in which the material ispre-tensioned during the introduction of the helical formation.
 7. Amethod according to claim 6, in which the material is pre-tensioned to10% of its maximum extensibility.
 8. A method according to claim 1, inwhich a second material is applied to the material after the settingoperation.
 9. A method according to claim 8, wherein the former createsan indentation in the external side wall of the material and the secondmaterial is applied to the indentation.
 10. A method according to claim9, wherein the second material overflows the indentation.
 11. A methodaccording to claim 8, wherein the coating is a polyurethane dispersion.12. A method according to claim 8, wherein the second material ispressed into the tubular material.
 13. A method according to claim 12,wherein the second material does not penetrate the material to theinternal side wall.
 14. A method according to claim 13, wherein thesecond material penetrates at least 50% but less than 100% into the sidewall of the material.
 15. A method according to claim 14, wherein thesecond material penetrates 80% to 90% into the side wall.
 16. A methodaccording to claim 1, in which a strand of a third material having adifferent modulus of elasticity to the tubular material is introducedinto and secured in the helical formation after the setting operation.17. A method according to claim 16, in which the strand materialcomprises a monofilament.
 18. A method according to claim 16, in whichthe strand material comprises a multifilament strand.
 19. A methodaccording to claim 16, in which the strand is secured by applying acoating to the tubular material.
 20. A method according to claim 1,further comprising forming a concertinaed formation in the tubularmaterial.
 21. A tube for a human or animal body, the tube comprising aflexible tubular material, a side wall of the tube being deformed toform a helical formation in the internal surface of the side wall of thetube.
 22. A tube according to claim 21, the tube comprising anindentation in the external surface of the side wall, and a coatingapplied to the indentation.
 23. A tube according to claim 22, whereinthe coating penetrates the side wall of the tube.
 24. A tube accordingto claim 23, wherein the coating only partially penetrates the sidewall.
 25. A tube according to claim 22, wherein the coating comprises apolymeric material.
 26. A tube according to claim 25, wherein thepolymeric material comprises polyurethane.
 27. A tube according to claim20, wherein the flexible tubular material is a woven material.
 28. Atube according to claim 20, wherein the flexible tubular materialcomprises polyester.
 29. A tube according to claim 20, wherein the tubeis blood flow tubing.
 30. A tube according to claim 29, wherein theblood flow tubing is a graft.
 31. A tube according to claim 30, whereinthe graft is a vascular graft.